Fix images in zonal stats notebooks (#438)

Author: dcherian

docs/source/user-stories/large-zonal-stats.ipynb

@@ -188,13 +188,13 @@
     "\n",
     "### reindex = True\n",
     "\n",
-    "<img src=\"../../diagrams/new-map-reduce-reindex-True-annotated.svg\" width=100%>\n",
+    "<img src=\"../_images/new-map-reduce-reindex-True-annotated.svg\" width=100%>\n",
     "\n",
     "First, the grouped-reduction is run on each chunk independently, and the results are constructed as _dense_ arrays on the full 23 x 5 x 7 x 248 x 86 x 854 output grid. This means that every chunk balloons to ~50GB. This method cannot work well.\n",
     "\n",
     "### reindex = False with sparse intermediates\n",
     "\n",
-    "<img src=\"../../diagrams/new-map-reduce-reindex-False-annotated.svg\" width=100%>\n",
+    "<img src=\"../_images/new-map-reduce-reindex-False-annotated.svg\" width=100%>\n",
     "\n",
     "First, the grouped-reduction is run on each chunk independently. Conceptually the result after this step is an array with differently sized chunks. \n",
     "\n",